1. Field of the Invention
The invention relates to a system and a method for locating a rail vehicle at points along a rail track equipped with a system of beacons. It relates more particularly to a system for accurately locating a rail vehicle relative to a beacon transmitting an electromagnetic signal conveying information. The invention also relates to an antenna adapted to be fitted to a rail vehicle in the system.
2. Description of the Prior Art
Equipping rail transport networks with a system of beacons on the ground for transmitting information between the beacons and equipment on board the vehicle is known in the art. The document FR-A-2 713 754 discloses a system of beacons on the ground, powered by radiation and enabling communication with an antenna on board a rail vehicle. Using a system of beacons for locating the rail vehicle on the track from the known location of the beacon that the antenna on board the rail vehicle is passing in addition to transmitting information is known in the art. Location is usually effected by analyzing the power of the signal picked up by the antenna. The moment at which the signal picked up by the antenna is at a maximum coincides with the moment at which the antenna is located above the beacon.
However, this kind of location method provides only relatively inaccurate location of the vehicle, the signal picked up by the antenna being at a maximum over a relatively wide range to enable information to be transmitted. In the EUROBALISE system employing beacons approximately 50 cm long, the accuracy in locating the vehicle is of the order of xc2x120 cm for a vehicle speed less than 40 kph and of the order of xc2x11 m for a vehicle speed greater than 300 kph.
This is not accurate enough for automatic vehicle control systems, in particular automatic vehicle control systems for a metro, which require an accuracy generally better than xc2x15 cm for correctly positioning the metro relative to the platform in stations.
The object of the present invention is therefore to propose a system and a method for locating a rail vehicle precisely relative to a system of beacons, in particular EUROBALISE beacons, which is simple and economical to implement.
The invention provides a system for locating a rail vehicle at points along a rail track equipped with a system of beacons, the beacons being adapted to convey information to the vehicle by transmitting an electromagnetic signal, the vehicle including an antenna having a first receiver circuit for picking up electromagnetic signals transmitted by the beacon when the antenna passes it, the antenna including a second receiver circuit in the form of a figure-of-eight loop for accurately determining the moment at which the antenna is centered over the beacon.
The invention also provides a system for locating a vehicle having any of the following features:
the first receiver circuit is in the form of a simple loop;
the beacon is powered by radiation and includes an antenna circuit picking up energy radiated by a transmitter on board the rail vehicle and supplying the necessary energy to a transmitter circuit of the beacon;
the beacon includes a transmitter circuit consisting of a loop and the external size of the figure-of-eight loop forming the second receiver circuit is substantially equal to the size of the loop of the transmitter circuit of the beacon;
the second receiver circuit is centered on the first receiver circuit so that the crossover point of the figure-of-eight loop forming the second receiver circuit is substantially at the center of the loop forming the first receiver circuit;
the system of beacons conforms to the EUROBALISE standard.
The invention also provides a method of locating a vehicle equipped with a system having any of the features defined above in which the phase shift of the signal delivered by the second receiver circuit relative to the signal delivered by the first receiver circuit is detected in order to deduce therefrom the moment at which the antenna is centered over the beacon.
The invention also provides an antenna for picking up electromagnetic waves transmitted by a beacon, the antenna including a first receiver circuit in the form of a simple loop for receiving information communicated by the beacon and a second receiver circuit in the form of a figure-of-eight loop for determining the precise moment at which the antenna is centered over the beacon.
According to one feature of the antenna according to the invention, the antenna is on board a rail vehicle and cooperates with beacons conforming to the EUROBALISE standard.
Aims, aspects and advantages of the present invention will become clearer after reading the following description of one embodiment of the invention, which description is given by way of non-limiting example and with reference to the accompanying drawings.